Opening a can of worms

June 26, 2021 0 Comments

This post first appeared on September 5, 2012
I intended to post another example of reverse dapple roaning, but an interesting development in an obscure pony breed – and an unrelated discussion on an online forum – convinced me it was probably time to air this topic.

For some time I have flirted with an idea that is quite simply heretical in horse color circles. Something so far out there, that only the most uniformed horseman might entertain such a notion. But evidence is evidence. If the evidence does not fit universally held beliefs, then it is time to examine those beliefs even if it does give some people heartburn.

So what is so beyond the pale in the horse color world? What have some researchers noticed, but feared to mention?

The tobiano pattern is sometimes associated with white markings on the face.

There. I have said it. I have noticed it for some time, as have others that were looking at some of the same breeds, or closely related breeds.

This was not something I was looking to find. What I was looking for was clues that some of the old Nordic or Celtic pony breeds still had splashed white. Most of these are breeds that either did not originally have “ordinary” markings, or where white markings – but not pinto patterns – were systematically bred out of the population. Quite a few of those breeds have classic splashed white (SW1), so it was reasonable to suspect that the horses with white on the face were heterozygotes (Sw1/n). Furthermore, it seemed likely that such a pattern could “hide” in the tobiano populations of the breeds where that was allowed, since few people minded if there were markings on a horse that already had a pinto pattern. The problem was that the expected SW1/SW1 homozygotes – the splashes with the classic pattern – never seemed to materialize. What’s more, when these ponies were crossed on solid mates, the face markings rarely appeared unless the tobiano pattern was also there. Even more tantalizing to someone looking for splash, these same ponies threw occasional blue eyes as well as the face white and the tobiano pattern. (I guess that counts as my second heresy in one post…)

I should clarify that I was looking at pretty unusual breeds. In the United States, it is quite difficult to find a popular breed without white markings of some kind. Most New World breeds not only have white markings, but many have what could be called sabino markings. In these breeds, like the Paint Horse pictured at the top, it is quite reasonable to assume that sabino (or splash or frame) are involved when a tobiano has a lot of white on the face. The question really is whether it is possible to get white on the face of a tobiano without these, or without the basic genes for white markings.

And now that question is being asked quite openly in a controversy surrounding the ancient Hucul Pony.

he Hucul is a primitive pony breed from the Carpathian Mountains. Most are dun, but tobiano is also a traditional color within the breed. Earlier this year, the parent stud book in Poland proposed separating out the tobiano Hucul population into a separate stud book. The reason? Because the tobiano ponies often have white on the face. It was feared that with the growing popularity of the tobiano pattern, the solids were in danger of having markings.

[Polish and Hungarian officials] claimed that piebald Huzuls transmit markings in a greater extent and these markings were undesired. Both recommend that piebald stallions may not cover plain mares. It is proposed to administrate piebald Huzul horses in a separate studbook.

There has been an outcry among breeders of tobiano Hucul Ponies that this fear is baseless because the leg markings on a tobiano are part of the pattern, which is permitted. The face markings, it has been noted, do not seem to pass along to the solids. This has lead to a discussion about the connection between face markings (and blue eyes) and the tobiano pattern. Some of the excerpts from this discussion are interesting:

This is from the paper “Odmiany a srokatosc” (Markings and Piebald) by Anna Stachurska. The emphasis is mine.

Anna Stachurska

Piebald Huzuls have the Tobiano gene, plain coloured Huzuls have not, even if they have piebald parents. Piebald Huzuls may have more markings because the Tobiano gene is located near one important gene for markings and the properties of genes in neighbourhood usually show up together. But this does not matter as piebald Huzuls have white spots anyway. In plain coloured Huzuls, even if they have piebald parents, an absent Tobiano gen cannot influence the appearence of a gene for markings. This means that plain coloured Huzuls with piebald parents need not to have more markings than Huzuls at all.

In clarifying her paper, she also writes this.

I would not write that tobianos have non-piebald head. In American publications tobianos are described as “conservatively” marked on the head or “with minimal extent of markings” on the head. However, in Poland tobiano halfbred horses (e.g. Wielkopolski, Małopolski) have rather big markings on the head, even with a glass-eye, though the markings are not bigger than “normal” (usual).

There has been some research on the subject of markings in recent years, notably one of the Franches-Montagne. From these discussions, it appears that there is more research being done. It is certainly too early at this point to say why tobianos in otherwise solid, unmarked breeds have a higher incidence of white on the face, but it does look like the subject has attracted some attention. Resolving the conflict between the different Hucul stud books may help provide some incentive to research this situation in more detail.

(Huzul group picture from Wikimedia Commons.)

By lkathman